Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
  • C10G9/00—Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils
  • C10G9/002—Cooling of cracked gases
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
  • C10G9/00—Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils
  • C10G9/14—Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils in pipes or coils with or without auxiliary means, e.g. digesters, soaking drums, expansion means
  • C10G9/16—Preventing or removing incrustation

Definitions

• the steam cracking process is the basic process of petrochemicals. It consists in thermally cracking a mixture of hydrocarbons and water vapor at high temperatures of the order of 850 ° C and then quenching the effluents in an indirect quenching exchanger generally designated by TLX or TLE (transfer line exchanger) then fractionating the cooled effluents.
• TLX transfer line exchanger
• the main operating problem of this process comes from parasitic deposits of coke in the pyrolysis tubes and those of the quench exchanger.
• a steam cracking process has already been proposed with the injection of erosive solid particles (powders), to remove at least part of the coke deposits.
• the particles are injected "in line", that is to say either during the normal steam cracking operation, or during phases in which the supply of hydrocarbons, the hydrocarbons, are temporarily and briefly interrupted (conventionally for a period of less than two hours). ovens being swept by steam alone, and remaining connected to the downstream sections for processing cracked gases.
• the preferred operating mode consists in injecting the particles during the normal operation of the oven, possibly by temporarily increasing the volume flow rate of the cracked gases, at the time of the injection of the powders, to increase their efficiency.
• ovens there are a plurality of ovens, each comprising, in general, several effluent quench exchangers (TLE); for example, there may be 10 ovens each comprising two TLE, or a total of 20 TLE operating in parallel.
• TLE effluent quench exchangers
• the number of receiving silos and or modules for processing the powders recovered for recycling can be limited to a maximum of two.
• a single reception and / or treatment module for the recovered powders will be chosen, if possible, common to the entire steam cracking installation.
• the effluents of each of the TLEs can be sequentially directed, at the time of the corresponding injection of the powders upstream of the TLE considered, towards a single cyclone for the recovery of the particles carried by the cracked gases (injected powders and coke particles eroded from the walls); this allows to install only a single cyclone of medium size, whose treatment capacity corresponds to cracked gases coming from a single TLE and not from all of the TLE of the steam cracker, but requires the installation of sets of valves relatively large diameter allowing the effluents of each of the TLEs to be oriented either towards the downstream sections of the steam cracker when no powders are injected upstream of this TLE, or towards the single cyclone when powders are injected upstream of this TLE.
• This variant process and installation therefore avoids installing a cyclone of very large capacity, inefficient, and often impossible to install on many existing steam crackers, but is however very expensive, because it requires a large number of special valves of large diameter (for example 20 valves for a steam cracker comprising 10 TLE).
• the junction lines between the exits of the various TLEs and the single cyclone are lines of relatively large diameter (250 to 300 mm also, in general), necessarily made of alloy steel because conveying cracked gases of high temperature typically 450 ⁇ C at 530 ⁇ C at the end of the cycle.
• a first objective of the method according to the invention, and of the corresponding installation is to propose a technical solution which is both reliable and inexpensive to this problem of collecting at a single point the powders circulating in the steam cracking effluents, when the 'anti-coking agents such as erosive powders are injected.
• a second objective of the method according to the invention, and of the corresponding installation is to solve this same technical problem when injecting another type of anti-coking agents, without significant erosive action, but also causing the circulation of particles and unwanted solid fragments.
• the object of the invention is therefore to propose a steam cracking process, benefiting from a general technical solution, reliable and economical, making it possible to separate and recover at a single point solid particles conveyed by the cracked gases, generated by various types anti-coking agents.
• the invention therefore proposes a process for steam cracking of hydrocarbons in an installation comprising at least one steam cracking furnace, this installation comprising a plurality of cracking zones, and a plurality of quenching exchangers (TLE) for the cracked gases. from these cracking zones, the process comprising the online injection, at a plurality of points, of decoking agents generating the circulation of solid particles in the said exchangers of quenching, and comprising the separation of at least part of these solid particles from the gases which contain them and their routing at a single point to common collection means for this installation.
• TLE quenching exchangers
• At least a portion of said particles are separated from the effluents of said quench exchangers, in a plurality of primary gas / solid separators,
• At least part of the particles thus separated from the said primary separators are recovered by gravity flow in a plurality of receiving canisters V ⁇ Vn, each can Vi being associated with at least one primary separator.
• each of the receiving canisters Vi is sequentially isolated from the associated primary separator (s) and then pneumatically the largest at least part of the particles contained in the canisters Vi is transferred to the said common collection means by means of a gas.
• non-coking transport and atmospheric dew point below 110 ° C the flow q ⁇ of transport gas for the evacuation of particles contained in a can Vi being less than or equal to 30% volume of the flow of cracked gases passing through the separators primaries associated with Vi.
• the particles are separated from the cracked gases which contain them or possibly a stream of water vapor alone in a plurality of primary gas / solid separators.
• the particles are no longer routed to the common means of collection by the cracked gases but by a "clean" gas, non-coking, substantially incondensable at average temperatures.
• these particle transport lines can be relatively cold, non-insulated lines, generally made of carbon steel, without any fear of coking problems or of tar condensation. These lines are therefore much less expensive than in the methods previously described. Furthermore, the risks of particle sticking in the presence of liquid condensation and of clogging of the lines are eliminated, which is a major advantage.
• the gas flow conveying the particles is disconnected from the cracked gas flow, and can be much lower, for example 30% or even less than
• the particles transferred from a can Vi are extracted from this can by exclusively pneumatic means.
• This extraction mode which carries out a pneumatic evacuation of all the particles contained in the container (except any large fragments mechanically blocked by a grid) by pressurizing the container and supplying transport gas at the outlet, is very reliable, in comparison with mechanical extraction by screw or lock, components which can be blocked by large solid fragments, or sometimes present flow problems of the "bridging" type, with the formation of arches " powders.
• Vi canisters as a pneumatic airlock, a technique known to those skilled in the art in other industries, with handling of powders and removal of the particles by the transport gas, significantly increases the reliability. of the process according to the invention, compared to the process previously described.
• the canisters Vi are heated by thermal means whose temperature level is between 110 ° C and 340 ° C, preferably between 150 and 250 ° C, this level remaining above the dew point of the gas of transport at the maximum operating pressure of the Vi canisters.
• temperature level is meant the condensation temperature of the vapor, when using steam tracing, or the maximum temperature level that can be maintained if using electric tracing.
• the lower limit temperature of said thermal means (110 ° C. in general and preferably 150 ° C.) aims to avoid any condensation of dilution vapor (entrained with the powder) or of fractions of pyrolysis gasoline.
• the average flow rates of particles on a steam cracking cycle are always very low compared to the flow rate of cracked gases (less than 1% and generally less than 1 per thousand), the capacity the calorific value of these particles is low, and they are rapidly cooled substantially to the temperature of the can Vi, which is determined by the temperature level of the thermal heating means of Vi. So the particles are stored, temporarily, at a temperature below the melting temperature of the pyrolysis tars.
• This percolation (crossing of the bed of particles) by a "dry" gas makes it possible to "strip” these particles and to better eliminate any traces of liquid present.
• it is possible to carry out a final drying of the particles during their pneumatic transfer in particular by maintaining the temperature of the particle / transport gas mixture, at the end of the pneumatic transfer for example in the gas / secondary solid separator , at a value between 40 ° C and 180 ° C, and preferably 80 to 150 ° C.
• These temperatures can be used when using an incondensable transport gas at room temperature (for example nitrogen or fuel gas), which is preferred. If steam is used as the transport gas, these temperatures should be raised significantly above the water vapor condensing point at the pressure of the secondary separator.
• This final drying in a fluidized bed circulating during the pneumatic transfer makes it possible to further improve the flow quality of the particles to a very high level. It will be very advantageously used when the particles are recycled, at least in part.
• the preferred transport gases are the condensable gases at normal temperature and pressure, in particular those chosen from the group of nitrogen, methane, hydrogen, light hydrocarbons comprising from two to four carbon atoms, and mixtures of these compounds.
• the available gases such as nitrogen, or fuel gas from the steam cracker (variable mixture of methane and hydrogen) are the most suitable. They allow the use of cold pneumatic transfer lines, generally not insulated.
• the decoking agents can be injected during phases when the supply of hydrocarbons to the cracking zone upstream of a TLE is interrupted (circulation of water vapor only).
• the preferred variant of the method consists in injecting the decoking agents during the normal operation of the installation, that is to say during the steam cracking phase at normal flow rate, or possibly temporarily increased by 10 to 50% by volume, in the case where solid erosive particles are introduced whose efficiency is to be increased.
• decoking agents two main types of effective agents can be used:
• the decoking agents comprise erosive solid particles, injected upstream of the quenching exchangers, in particular in the cracked gas transfer zones comprised between the outputs of the cracking zones and the quenching exchangers.
• the average particle diameter can be between 0.02 and 4 mm, and preferably between 0.07 and 0.8 mm.
• the particle size must be reduced, less than 150 micrometers, to approximate an erosive gas effect.
• the particles are injected at the inlet of the TLEs, to strip the coke from these TLEs and to obtain a very high flexibility of the cracking charges going from very light to very heavy loads, we can use particles of larger diameter, typically between 70 and 800 micrometers: indeed, the TLE do not include bends or changes of direction, but only straight lengths, and we is not afraid of concentration of impacts by particles which may cause local erosion.
• the usable particles are very variable, from the moment they have an erosive efficiency. For this reason, it is recommended to use at least 20% of angular (or very irregular) particles.
• As regards the composition of these particles it is possible to use for example spent fluid cracking catalyst (FCC), cement clinker, crushed ores, metallic particles, sand.
• Particularly interesting particles are hard and not very fragile mineral particles such as silicon carbide, or simple or mixed oxides of aluminum, silicon and zirconium.
• Other very interesting particles are coke particles, in particular coke particles stabilized by calcination at 850 ° C. or more, carried out before or after their grinding. These coke particles are more fragile and less effective than mineral particles, and must be injected in increased quantities.
• Such a coke trap can be constituted by an abrupt change in direction of the flow of cracked gases, for example a simple, non-cyclonic deflection, of the flow at an angle between 30 and 180 ° C., for the evacuation of at least most of the cracked gases, and a particle recovery chamber situated at the level of the sudden change of direction, or downstream, connected by a narrowing to a container for receiving the particles according to the invention.
• Particle injections are preferably carried out sequentially, that is to say discontinuously.
• a dose of particles is injected at fixed or variable intervals of between 0.3 and 72 hours and preferably between 1 and 20 hours, successively upstream of the various TLEs equipped according to the invention.
• the instantaneous quantity of particles, by ratio to the cracked gases is between 0.5 and 25% by weight, in particular between 1 and 10% by weight. If we compare the total amount of particles injected during a steam cracking cycle with the total amount of cracked gas during this cycle, the average particle levels are then much lower, because we do not injects particles only for a small fraction of the time.
• the average level of solid particles injected during a steam cracking cycle, with respect to the cracked gases is less than 3000 ppm, and generally between 20 and 1500 ppm.
• At least part of the particles recovered in the common collection means are recycled, by reintroducing these particles upstream of at least one of the quench exchangers, after having carried out a screening operation, carried out at least on this said part of the particles recovered in the common means.
• the screening operation can be carried out at atmospheric pressure and under an atmosphere essentially of nitrogen. It is also possible to screen the particles without depressurizing them and then recycling them, for example, using fuel gas.
• Particle recycling at least partially, has already been described previously; it reduces consumption of "new" particles.
• the characteristic arrangement of the recycling process according to the invention consisting in carrying out, after the pneumatic transfer of the particles by an incondensable gas, a screening step at atmospheric pressure, under nitrogen, is of very great interest:
• the invention makes it possible, by this pneumatic transport, to carry out both drying and cooling of the particles in a circulating fluidized bed.
• This makes it possible to use existing, economical and very reliable screens, such as screens, also called screens, centrifuges, or preferably vibrating screens.
• the flexible connecting cuffs of these devices made of possibly reinforced elastomer, would be incompatible with the particles at very high temperature (400 ° C. or more), which pass through the filter of the process previously described.
• this filtration step is essential to avoid the risk of clogging of the recycled powder injectors which have a small diameter.
• the screening being 1 2
• the fragments (coke and foreign bodies) with a diameter greater than 3 or 4 mm are eliminated.
• the decoking agents comprise mineral salts catalysts for gasification of coke by water vapor, injected upstream of the cracking zones.
• these mineral salts can comprise at least one salt of an element included in the group of sodium, potassium, lithium, barium and strontium, this salt being active to promote the gasification of coke.
• mixtures with a melting point lowered below 750 ° C. for example close to eutectics
• sodium carbonate and potassium carbonate have a very effective action for coking or preventing coking.
• acetates can also be used, for example an equimolar mixture of sodium acetate, potassium acetate, lithium acetate and barium acetate.
• These compounds can catalyze the gasification reaction of coke (in particular the reaction of "gas to water”: C + H2O -> CO + H2); they can be introduced in the form of powder or in the form of aqueous solutions, in particular very dilute solutions, atomized in a hot gas, and in particular in the dilution water vapor, or the water vapor / hydrocarbon mixture in convection outlet (at a high temperature of the order of 500 to 650 ° C).
• the preferred injection mode is injection during normal steam cracking operation; it is also possible to inject these mineral salts only during decoking phases with water vapor alone, in particular to accelerate this decoking.
• the amount required depends on many factors: the nature of the compounds used and the load to be cracked, severity of cracking and skin temperature of the pyrolysis tubes.
• the most suitable amounts are typically between 2 and 200 ppm, and preferably between 5 and 100 ppm, calculated by weight of alkaline and / or alkaline earth elements relative to the cracked gases.
• the invention also relates to a steam cracking installation making it possible to implement the method. More specifically, this installation comprises at least one steam cracking furnace, a plurality of cracking zones, a plurality of heat exchangers for quenching the cracked gases coming from these cracking zones, this installation also comprising injection means in a plurality of points, of decoking agents generating the circulation of solid particles in the quenching exchangers, a plurality of gas / solid primary separators, for the purification of the effluents of the quenching exchangers, each primary separator being connected upstream to at least one quench exchanger associated therewith and comprising an outlet for purified gases and an outlet for solid particles, and means for recovering at least part of these solid particles, these recovery means comprising common means for separation and collection gathered at a single point,
• each canister Vi being connected to at least one outlet of solid particles of at least one primary separator associated with Vi,
• pneumatic means for the transfer, by the said transfer pipes, for at least most of the particles contained in the canisters Vi thus isolated, these pneumatic means comprising means for supplying a non-coking transport gas and with an atmospheric dew point below 110 ° C, at a flow rate qi, for the evacuation and transfer of particles contained in a can Vi, less than 30%, by weight of the gas flow rate passing through the primary separators associated with Vi.
• the primary separators individually have a relatively small unit capacity compared to the overall cracked gas flow rate of the entire installation, and are therefore efficient and easy to install. They carry out an effective purification of the cracked gases not only during the solid particle injection phases, according to the method described above, but also permanently, and are therefore also effective with respect to the emissions of solid particles after phases of injection of decoking agents. This is useful both for the residual particles circulating after injection phases of erosive particles which have remained in the dead zones, as well as when the chemical agents for gasifying the coke are injected.
• any additional large diameter valve typically greater than 150 mm
• sequential isolation is meant an alternation of phases where a receiving can Vi is in communication with upstream, and phases where it is isolated from upstream to allow evacuation downstream, to the common means of separation and collection. This will preferably, but not necessarily, be done in a coordinated manner for the different canisters Vi, each of these canisters can be isolated successively, so as to stagger the transfers. It is indeed also possible to empty several Vi canisters simultaneously.
• the common means of collection typically consist of a container making it possible to temporarily or temporarily store the particles, which may possibly include weighing means.
• a quench exchanger is said associated with a primary separator if this primary separator purifies the effluents from this quench exchanger.
• a primary separator is said to be associated with a receiving can Vi if Vi recovers, by gravity flow, at least part of the particles separated in this primary separator.
• a primary separator can be associated with one or more quench exchangers, from which it purifies the effluents; a receiving can Vi can collect particles from one or more primary separators.
• the installation can in fact comprise at least two primary separators associated with the same receiving container, each of these primary separators being connected to this container by a pipe, and comprising control means means for sequentially closing off at least one of the pipes when the other of these pipes is open, the relative arrangement of these primary separators and of the receiving container being such that the pipes have an inclination at least equal to 60 degrees from the horizontal.
• This arrangement makes it possible to use a single can Vi for the reception and transfer of particles coming from several primary separators, and is therefore advantageous economically, and from the maintenance point of view.
• the sequential isolation of at least one of the pipes makes it possible to avoid the circulation of cracked gases via the canister Vi from one primary separator to the other, detrimental to the separation efficiency.
• the evacuation of the particles contained in a canister Vi is carried out by means of emptying, connected to Vi, which are exclusively pneumatic, and use at least one source of gas from the group of nitrogen and fuel gas. (methane or mixture of methane and hydrogen).
• These pneumatic emptying means by "pneumatic shipping lock”, or “pressurized container”, and which typically comprise a pressurization of the container Vi with respect to the conditions downstream of the pneumatic transfer line and an injection of transport gas in exit Vi, are indeed very intense, and allow to evacuate powders presenting flow difficulties; they are more effective than the evacuation means of the process previously described.
• the flow rate of transport gas making it possible to transfer the particles is only 30% at most of the flow rate of gas passing through the primary separators associated with Vi during the same period, typically the normal flow rate of gas cracked treated by the primary separator (s) whose particles fall into Vi.
• the transfer line is therefore much smaller in diameter than that of cracked gas lines (less than or equal to 100 mm against typically 250 to 400 mm).
• this transport gas is fuel gas or nitrogen, gases which are noncondensable at ambient temperature, and which will allow drying of the particles during their transfer.
• the canisters Vi are heated by thermal means whose temperature level is between 1 10 and 340 ° C, and preferably between 150 and 250 ° C. This temperature level, which corresponds to that of the condensation temperature of the heat tracing vapor, or of the temperature maintained by electrical means, is in fact adequate for maintaining pyrolysis tars in the solid state.
• the installation comprises means for sweeping the gas contained in the canisters Vi, by means of a source of non-coking gas and an atmospheric dew point below 110 ° C.
• This scanning which by technical equivalent can be constituted by a barrier gas, has the function of purging Vi of possible traces of cracked gases, before the evacuation and the transfer of the particles.
• the installation comprises means for introducing a non-coking gas and an atmospheric dew point below 110 ° C., within the particles contained in the canisters Vi, for percolating these particles before their evacuation from the Vi drums.
• the decoking agents comprise erosive solid particles, and means for injecting these particles upstream of the quench exchangers, and in particular in the transfer zones between the cracking zones and the quench exchangers.
• all of the solid particles injected are in the cracked gas transfer zones between the cracked zones and the quench exchangers, in particular in the inlet cones of these exchangers (considered to be part of the transfer areas).
• the common separation means which carry out a secondary separation of solid particles / transport gas which is substantially incondensable comprise an outlet for purified transport gas connected by a connection line to a line for the circulation of cracked gases, for the evacuation of this purified transport gas.
• the transport gas is then fuel gas, which avoids the consumption of nitrogen and its significant mixing with the cracked gases.
• the installation comprises means for recycling at least part of the particles recovered in the common means of separation and collection.
• the installation then comprises a vibrating screen operating under a nitrogen atmosphere at substantially atmospheric pressure and at a temperature below 200 ° C., connected upstream to the common means, of separation and collection and connected downstream to the means for recycling particles.
• the installation comprises means for injecting decoking agents, comprising chemical compounds which are catalysts for gasifying coke with water vapor, upstream of the cracking zones.
• decoking agents comprising chemical compounds which are catalysts for gasifying coke with water vapor, upstream of the cracking zones.
• such an installation may advantageously comprise means for injecting a solution comprising at least one mineral salt of an element included in the group of sodium, potassium, lithium, barium and strontium, this salt being active. to promote the gasification of steam coke of water, this gasification weakening the coke and causing emissions of pieces of coke, which can be recovered and transferred according to the means of the invention.
• the invention may include means for sequential injection of erosive particles connected to said transfer zones, means for sequential isolation of each can Vi outside of the particle injection phases. upstream of Vi, and means for evacuating the particles recovered in the separator (s) associated with Vi outside these injection phases, without passing through Vi.
• the installation may typically comprise canisters Wi for receiving particles recovered outside the particle injection phases, and directional switches controlled at one input and two outputs, each switch being connected upstream to a primary separator , and downstream to a receiving can Vi, and to a receiving can Wi.
• FIG. 1 schematically represents a steam cracking installation according to the invention, comprising several devices relating to different characteristic variants according to the invention.
• FIG. 2 schematically represents a part of an installation comprising a device characteristic of one of the variants of the invention.
• FIG. 3 represents a part of an installation comprising another characteristic device, advantageous for carrying out the invention.
• FIG. 1 where there is shown, in part, two steam cracking furnaces (1) each comprising a supply (22) of a hydrocarbon charge and a supply (23) of steam dilution water.
• the overall charge is preheated, vaporized and superheated to a typical temperature of 500 to 650 ° C in the convection zones of these two ovens, then cracked in two cracking zones (2) constituted by coils of pyrolysis tubes.
• the cracked gases pass through transfer zones (3) to two quench exchangers (4), or "TLE" (Transfer Line Exchanger ) allowing their temperature to drop suddenly to around 360 to 630 ° C, and very generally to around 360 to 500 ° C, this temperature being measured by temperature indicators (24).
• TLE Transfer Line Exchanger
• These two cooled cracked gas streams then pass through two primary gas / solid particle separators (5), for example two cyclones.
• Each of these primary separators comprises a purified gas outlet which joins a line (12) for the circulation of cooled cracked gases, for their evacuation and their downstream treatment (primary fractionation, compression, desulfurization, drying, final fractionation).
• the two primary separators (5) also each include an outlet for solid particles connected by a pipe (16) to a receiving container (6) maintained at temperature by thermal means (37), for the recovery of these solid particles by flow. gravity.
• the two receiving containers (6) each comprise sequential isolation means: upstream a controlled valve (7) disposed on the line (16), and downstream a controlled valve (8). These two receiving drums (6) are connected downstream, each by a transfer pipe (9), to common means for separating and collecting solid particles, comprising a separating cyclone (10) and a collecting can ( 13). The cyclone effluent gases (10) are introduced into the line (12) through a line (11).
• This collection container (13) is connected downstream by a line (32) to a vibrating screen (14) connected to the atmosphere by a line (ATM) operating substantially. at atmospheric pressure, under a nitrogen atmosphere, and at moderate temperature compatible with flexible connection sleeves used for conventional vibrating screens.
• the container (1) which includes upstream and downstream isolation valves, as well as means (not shown) for depressurization, fulfills the function of airlock for decompressing particles.
• the outlet of fine particles from the vibrating screen (14) (particles cleared for example of large fragments of dimension greater than 3 mm) is connected to a receiving container (15), equipped with valves controlled upstream and downstream, as well as means of 'supply, not shown, of gas from the nitrogen group and fuel gas.
• a receiving container equipped with valves controlled upstream and downstream, as well as means of 'supply, not shown, of gas from the nitrogen group and fuel gas.
• the vibrating screen (14) will be placed above the can (15), to allow the gravitational flow of the powders (this is not the case in FIG. 1 for simple drawing reasons).
• the can (15) thus equipped can then operate in a pneumatic shipping lock, and constitutes a means of recycling erosive solid particles in the installation. It is connected upstream to a source of transport gas (33) (fuel gas, nitrogen or water vapor), and downstream to various injection means (19) (34) comprising controlled valves and conduits of injection of solid particles.
• transport gas fuel gas, nitrogen or water vapor
• injection means (19) comprising controlled valves and conduits of injection of solid particles.
• the particles can be injected upstream of the cracking zones (2) by the lines
• a diffuser impactor (35) will preferably be installed inside each inlet cone. This diffuser impactor has a double purpose: to protect the tube plate in the quenching exchanger against erosion, and to distribute the injected particles more evenly, in the different tubes of the exchanger (4).
• This diffusing impactor (35) advantageously consists of two levels of particle rebound surfaces, offset with respect to each other, so that it is both permeable to gases in a plurality of passages and substantially opaque seen from upstream.
• the shipping lock (15) includes a line (36) for discharging used particles; we could also send the used particles to a storage silo thanks to a switch arranged on the line (32); a container (18) comprising means of controlled emptying (screw or lock) makes it possible to store "new" particles, and to replace the used particles.
• the installation also includes pneumatic means enabling particles to be transferred from the Vi canisters (6) to the common means of separation and collection, via the transfer pipes (9): a source (31) non-coking gas, dew point at atmospheric pressure below 110 ° C: water vapor or preferably nitrogen or fuel gas, allows:
• valve (25) using the valve (25) to inject such a non-coking gas with an atmospheric dew point below 110 ° C. to drain the gas contained in the receiving canister Vi (6), before evacuation and transfer particles, and pressurize the container (6) during the pneumatic transfer of the particles.
• the installation described in FIG. 1 finally comprises a programmable automaton (17) for controlling the sequential operation of the installation, in particular the valves of the pressure relief airlock and the airlock airlock. It also comprises means (20) for injecting upstream of the cracking zone (2) of chemical compounds which are catalysts for the gasification of coke by steam, for example aqueous solutions of an equimolar mixture of sodium carbonate. and potassium carbonate, or an equimolar mixture of sodium acetate, potassium acetate, lithium acetate and barium acetate.
• FIG. 2 where two quench exchangers (4), or “TLE”, are shown diagrammatically, the inlet cones each of which have a pipe (19) for injecting erosive solid particles.
• These exchangers are connected downstream to two primary separators (5) connected by lines (16) each comprising a controlled isolation valve (7), to the same receiving canister (6), which constitutes one of the canisters Vi of the installation, and is therefore associated with the two primary separators (5) shown.
• a transfer pipe (9), comprising a controlled valve (8) makes it possible to sequentially transfer the particles to common means (10),
• the container (6) operates in a pneumatic airlock, with pressurization of the airlock and evacuation of particles by a transport gas.
• the arrangement of the two primary separators (5) is not arbitrary, but these separators are installed sufficiently close together so that the connecting lines (16) with the single receiving container (6) are very inclined and form with the horizontal an angle ⁇ at least equal to 60 ° C.
• FIG. 3 shows a quenching exchanger (4) connected to a primary separator (5), itself connected to a receiving can Vi (6).
• This FIG. 3 also includes other technical elements already described previously and referenced in the same way.
• another container, Wi, (28) for receiving solid particles has been shown, also connected to the primary separator (5), and a controlled directional switch (29) (flap, valve or equivalent technical device), making it possible to 'orient the particles recovered in the primary separator (5), either towards the can Vi (6), or towards the can Wi (28).
• A- Injection of erosive solid particles Intermittent injections of erosive particles are carried out in the installation, by the means (19): controlled valves and injection pipes.
• particles can be injected through the lines (34) upstream of the cracking zones (2); when variable loads are cracked under flexible conditions, the particles are mainly, or exclusively, injected into the transfer zones (3) at the inlet cones of the quench exchangers; it has in fact been found that variable conditions at the level of the charges could lead to coking rates of the pyrolysis tubes which are difficult to predict and unsuitable for controlling particle injections in the cracking zones.
• the coke from the quench exchangers is, surprisingly, much easier to remove by erosion than that from the cracking zones. It is therefore possible to control the quantities of particles to be injected without carrying out prior tests, based on the outlet temperature of the quench exchangers.
• doses of fine erosive particles are injected discontinuously, each dose corresponding to a weight of particles typically between 5 and 150 kg, in particular between 20 and 100 kg.
• Two types of injection control are possible: according to the first type of control, particles are injected, at a given injection point, at a fixed time interval, for example every 3 hours. And the quantities injected are adjusted (for example by weighing means, not shown in FIG. 1), so that the increase in the outlet temperature of the quench exchanger concerned located downstream of the injection point remains moderate, for example less than 100 ° C per month and preferably 30 ° C per month or substantially zero.
• doses of constant quantities of particles are injected, but at variable time intervals, in order to limit or cancel the increase in the outlet temperature of the quench exchanger.
• the particles typically injected through a conduit (19) typically comprising at its end from 1 to 8 particle injectors in the inlet cone of a quenching exchanger (4) are entrained by cracked gases, rebound on the diffusing impactor (35), and are distributed in an improved manner in the different tubes of the exchanger (4), where they circulate at speeds between 20 and 180 ms and preferably between 35 and 120 m / s, and pickle part of the coke or heavy tars deposited on the walls of these tubes.
• the particles are then removed, in dense phase or in diluted phase, by the transfer pipe (9).
• the flow rate qi of transport gas for carrying out this transfer is according to the invention much lower than that of cracked gases passing through the primary separator (5).
• the line (9) is therefore of small diameter, as are the valves (7) and (8), because we have achieved, thanks to the change of gas carrying the particles: cracked gas -> dry clean gas (N2, fuel gas ), a decoupling with the cracked gas flow rate, necessarily very high.
• the line (9) and the valves (7) and (8) are of diameter less than or equal to 100 mm against 350 mm typically for the particle transfer lines of the method previously described.
• the line (9) is relatively cold, generally not drawn and not insulated on at least part and can be made of carbon steel.
• the transfer of the particles according to the invention is therefore particularly economical, and also reliable because it makes it possible to dry the particles, in the receiving canister Vi (6) then in a circulating bed, thanks to the transport gas, in the transfer pipe ( 9).
• This transfer pipe makes it possible to cool the particles (the heat exchanger with the colder walls of the line (9) being favored by circulation in the bed fluidized).
• the particles passing through the pipe (9) are therefore cooled to a typical preferred temperature of 80 to 150 ° C., a moderate temperature compatible with the vibrating screen, but sufficient to carry out any additional drying of the particles.
• These common means include a cyclone (10) for separating particles from the transport gas, and a container (13) for collecting the particles.
• the purified transport gas is returned by the line (11) to the line (12) for discharging the cooled cracked gases.
• the collection container (13) is isolated from upstream, depressurized by means not shown, and drained via line d 'evacuation (32). This emptying, for example gravity, is facilitated by the fact that the particles are dry and not sticky.
• the particles are then sieved through the vibrating screen (14), which removes fragments larger than 3 mm, and fall into the receiving container (15) whose upstream valve is open and the downstream valve closed.
• a first very coarse screening (mesh of 15 to 20 mm) can be carried out by means of a simple grid in the receiving containers (6) to avoid the risks of obstruction of the transfer pipes (9).
• the sieved particles When the sieved particles are in the can (15), they can then be recycled, by isolating the can (15) from upstream, and by injecting a pressurization gas and a transport gas, according to the same type of operation as the container (6): evacuation by airlock airlock according to several alternative embodiments, as for the airlock (6).
• the preferred transport gas is fuel gas, or nitrogen.
• Controlled valves included in the means (19) for injecting particles make it possible to select the injection point or points chosen, for example those whose quench exchanger has the highest outlet temperature.
• the container (15) also comprises means (16) for discharging used particles, with reduced erosive efficiency after a certain number of circulations. The dose of used particles is then replaced by new particles stored in the container (18), and transported by a supply of transport gas (33).
• FIG. 1 also makes it possible to inject chemical decoking agents by the means (20) which may comprise a reservoir of an active solution, and a metering pump. These compounds are injected continuously or discontinuously, finely sprayed into the cracked gases.
• the installation also includes a control module (17 see FIG. 2) such as a programmable automaton making it possible to operate all of the sequential actions automatically.
• a control module such as a programmable automaton making it possible to operate all of the sequential actions automatically.
• the device described in Figure 2 operates like that of Figure 1.
• the two valves (7) are however never opened simultaneously to avoid parasitic circulation between the two cyclones (5), via the lines (16).
• the particles are therefore injected into the two exchangers (4) during different phases, the corresponding valve (7) being the only one open during an injection.
• the minimum angle ⁇ of at least 60 ° ensures the gravity flow of the particles recovered.
• the device described in FIG. 3 operates as follows:
• the directional switch (29) is oriented as shown in the figure to allow the recovery of erosive particles in the receiving canister Vi (6).
• the switch is oriented in the opposite direction, so that the particles fall into the receiving Wi container (28).
• the particles of coke detached from the walls which can circulate spontaneously in the installation, or resulting from the embrittlement of the coke by the chemical compounds injected do not mix with the erosive particles, recovered in the container (6). This improves the operation and reliability of the installation.
• the particles contained in the effluents of the quenching exchangers are transported by these effluents to the general network for the treatment of cracked gases which comprises a single cyclone.
• the general network for the treatment of cracked gases which comprises a single cyclone.
• each outlet of a quenching exchanger comprises two controlled valves making it possible to direct the effluents either to the downstream network for processing cracked gases when no particles are injected, or to common means of separation and collection.
• This known installation makes it possible to transport the particles to a single point, by means of 20 additional lines of cracked gases, of 350 mm in typical diameter, and comprises 20 ⁇ 2, that is to say 40 special valves of large diameter capable of directing the cracked gases towards the right network.
• the cyclone on the other hand, has a reasonable capacity of 10,000 kg / h and is easily implantable and effective.
• This installation makes it possible to inject erosive particles, for example doses of 50 kg of angular coke, or angular silicon carbide, and to recover these particles in a common place. It allows, thanks to these injections to be able to avoid the fouling of the quench exchangers and to crack unconventional charges (kerosene, diesel, condensates) with cycle times greater than 1 month, which is not possible without injection of particles.
• erosive particles for example doses of 50 kg of angular coke, or angular silicon carbide
• most of the particles recovered are recycled.
• Example 2 which also includes 20 primary separators (cyclone (5)), but only 10 receiving Vi tanks (6), arranged in accordance with FIG. 2, and 10 transfer pipes (9) with a unit capacity of 1000 kg / h of fuel gas.
• Example 4 We always consider the same steam cracking installation, in which we install not 20 but 10 primary separators (5), each separator grouping the effluents from two quench exchangers (1 furnace). 10 Vi receiving cans and 10 transfer pipes (9) with a unit capacity of 1000 kg / h of fuel gas are used. This installation has a slightly lower particle recovery efficiency than that of Examples 2 and 3, but is economically inexpensive.
• Example 4 Consider the installation of Example 4, supplemented by means (20) for injecting 15 to 100 ppm of chemical compounds (by weight of sodium plus potassium) relative to the cracked gases, in an aqueous solution at 96% d 'water of equimolar composition of sodium carbonate and potassium carbonate. These compounds promote the gasification of coke from cracked zones, and also cause embrittlement of this coke and emissions of fragments detached from the walls.
• 10 switches (29) and 10 Wi receiving canisters (28) are installed in accordance with FIG. 3.
• the invention therefore provides a method and an installation, with several variants, making it possible to use effective decoking agents to allow cracking of charges that are impossible to crack under conventional conditions without excessive fouling, and to recover the solid particles generated by this implementation, more economically and more reliably than in the processes and installations previously described.

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• 1994
  • 1994-12-26 FR FR9415746A patent/FR2728580A1/fr active Granted
• 1995
  • 1995-12-22 EP EP95943262A patent/EP0801670B1/de not_active Expired - Lifetime
  • 1995-12-22 DE DE69515700T patent/DE69515700T2/de not_active Expired - Fee Related
  • 1995-12-22 ES ES95943262T patent/ES2145323T3/es not_active Expired - Lifetime
  • 1995-12-22 WO PCT/FR1995/001718 patent/WO1996020256A1/fr active IP Right Grant
  • 1995-12-22 US US08/836,147 patent/US5820747A/en not_active Expired - Fee Related
  • 1995-12-26 TW TW084113871A patent/TW309539B/zh active

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